In my case, the motivation is replayability in a way that the same game produces extremely different story arcs. I'd also have some story arcs available to some backgrounds that wouldn't be available to others.
Basically: I want to tell the story of this particular party.
Vs: I want to tell this particular story with this party.
Both valid and fun options, neither superior. Just different.
I talked about it before when this discussion came up, but what Larian are doing is also a way to increase replay value. A shitty cheap and lame way to do it, but still a way.
